Bye-Bye, PCs

As the PC era wanes, Dell and HP will fade from view. Tablets, smartphones, and big data will drive Apple, Google, and EMC.

When Microsoft introduces its long-awaited Windows 8 operating system Friday, it will be the first Windows rollout to face real competition since, well, forever. Today, smartphones and tablets do almost all of the day-to-day tasks a PC does -- including sending e-mail, surfing the Web, and editing photos -- and do some of them better. Already, tech investors, long accustomed to a lift from Windows, are primed for disappointment.

At the same time, big data -- massive data centers that can marshall tremendous computing...